Not a stupid question at all!
A general answer is that most early war aircraft were 'consumed' by that war (not scrapped) as 'there was a war on'! They were shot down, crashed, cannibalised, modified to later models, used and wrecked in training, and some were scrapped and the metal used for newer aircraft.
However when the allies got the upper hand the production lines were pumping out new aircraft right past the war's end. After the war, when it came to further use by other people, like airlines, sprayers, surveyors etc, they could (perhaps) choose a ratty old 'veteran' aircraft or a brand new one with no military service. A no-brainer really, so the cull of historic aircraft continued.
It's only much later that actual war history started to count for so much.
Hence the reason that flying P-51Ds, B-17Gs, late mark Spitfires, outnumber all the types used earlier; like small tailed B-17s, P-51A-C, early mark Spitfires, and why the huge range of early war types are almost extinct. But again it's getting better - a P-36 flying in Britain, and there's some real early model P-40s appearing rather than late ones wearing incorrect Flying Tigers colours. (Mutton dressed as lamb, and a personal hate of mine.

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